feat(release): add plain-text Description field plumbed CMS->DTO->release (11.G)

New nullable Description column (max 4000) on ReleaseEntity, rides the Genre write channel through upload + edit; multiline CMS input. Migration authored, not applied.

DeepDrftAPI/Services/UnifiedTrackService.cs

@@ -57,6 +57,7 @@ public class UnifiedTrackService
         string artist,
         string? album,
         string? genre,
+        string? description,
         DateOnly? releaseDate,
         long createdByUserId,
         string? originalFileName,
@@ -106,8 +107,8 @@ public class UnifiedTrackService
 
         // Resolve the release FK before persisting the track. An upload with an album lands on the
         // shared release (created on first sighting); an upload without one stays a loose track with
-        // a null ReleaseId. Release-cardinal metadata (artist/genre/releaseDate/type/uploader) rides
-        // on the release, not the track.
+        // a null ReleaseId. Release-cardinal metadata (artist/genre/description/releaseDate/type/uploader)
+        // rides on the release, not the track.
         long? releaseId = null;
         if (!string.IsNullOrWhiteSpace(album))
         {
@@ -116,6 +117,7 @@ public class UnifiedTrackService
                 Title = album,
                 Artist = artist,
                 Genre = genre,
+                Description = description,
                 ReleaseDate = releaseDate,
                 ReleaseType = releaseType,
                 Medium = medium,